United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/102 Nov. 1985
&ER& Project Summary
Organic Chemical Fate
Prediction in Activated Sludge
Treatment Processes
J. W. Blackburn, W. L. Troxler, K. N. Truong, R. P. Zink, S. C. Meckstroth, J. R.
Florance, A. Groen, G. S. Sayler, R. W. Beck, R. A. Minear, A. Breen, and0. Yagi
This project summary describes re-
sults from a broadly based effort to
determine the feasibility of predicting
the fates of organic chemicals in dif-
fused air. activated sludge wastewater
treatment processes. The three conver-
sion/removal mechanisms emphasized
in this work were stripping, sorption on
biomass, and bio-oxidation (biotransfor-
mation and mineralization). After an
initial literature review and critique,
separate projects were implemented to
study experimental and mathematical
predictive methods on each individual
fate mechanism and to develop exper-
imental and/or mathematical protocols
where needed. Finally, a project was
implemented to couple the mechanisms
in a semi-deterministic predictive equa-
tion and to attempt initial verification
for the equation in a continuous, com-
pletely mixed laboratory activated
sludge study.
Specific compounds studied in this
project include methyl ethyl ketone,
toluene, phenol, aniline, 1,4-dichloro-
benzene, 2,4-dichlorophenol, and pent-
achlorophenol. Only certain compounds
typical for the mechanism of interest
were studied in each mechanism proj-
ect. Both 14C-labeled and nonlabeled
compounds were used in the sorption,
bio-oxidation, and laboratory activated
sludge projects to provide independent
and corroborative analysis as well as an
unambiguous measure of bio-oxidation
mineralization.
Stripping studies in a coarse bubble
diffuser reactor determined the kinetic
relationships between compound Hen-
ry's law constants, liquid volume, and
air flow rate and the effects of contam-
inants on stripping kinetics. Sorption
studies used nonviable biomass in a
special variable-volume reactor to meas-
ure sorption equilibria and to estimate
sorption kinetics. Predictive equations
are proposed for stripping and sorption
processes.
Bio-oxidation kinetics for both bio-
transformation and mineralization were
determined for batch, fill-and-draw, and
continuous systems. First-and second-
order (first-order in both substrate and
biomass concentrations) kinetics were
formulated. Specific degrader and total
viable subpopulations were enumerat-
ed.
An algebraic, coupled, predictive
equation and related fate equations are
proposed for diffused air, completely
mixed activated sludge systems. Unver-
ified examples of the use of these
equations for fate prediction are also
presented.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati. OH, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The goal of this research was to eval-
uate the potential of developing a method
for quantitatively predicting the fates of
chemicals in an activated sludge plant—a
predictive fate method (PFM). For PFM
development, the theory behind the spe-
cific transport and conversion mechan-
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isms must be known and these mechan-
isms must be coupled into a combined,
dynamic model. Experimental data must
exist or be generated on each mechanism
to evaluate and verify the model. Collec-
tion of these data must be controlled so
that the effects of different mechanisms
can be analyzed separately. The model or
method must be extensively tested, ulti-
mately against full-scale data.
This project was conceptualized with
the following objectives:
1. To survey and assess the existing
data base related to stripping, bio-
mass sorption, and bio-oxidation
mechanism rate predictions.
2. To select a limited list of compounds
for study that might be indicative of
the behavior of many more organic
compounds.
3. To develop experimental protocols
to measure and quantify the kinetics
of stripping, sorption onto biomass,
and bio-oxidation.
4. To develop mathematical protocols
or models to describe the removal/
conversion rates for the stripping,
sorption,and bio-oxidation mechan-
isms.
5. To develop an overall experimental
protocol for measuring the mechan-
ism kinetic rates in a continuous
system more representative of real
operating activated sludge plants.
6. To develop an overall mathematical
protocol or model to incorporate the
individual mathematical predictors
and describe compound fates in a
complex system indicative of an
operating activated sludge plant.
7. To determine the feasibility of eval-
uating the kinetic rate and other
constants necessary for individual
or coupled mechanism fate predic-
tion from physical, chemical, or
structural properties of the com-
pound itself.
The literature was surveyed to deter-
mine the present level of understanding
of the relationships between chemicals
and their treatment in activated sludge
treatment processes. Treatability was
analyzed in terms of the basic removal/
conversion mechanisms of (1) bio-oxida-
tion, (2) stripping, and (3) sorption. In
some cases, other mechanisms such as
chemical oxidation, hydrolysis, or photol-
ysis become important. The first three
mechanisms were given priority in this
study.
Selection criteria were developed and
applied to a large list of aromatic com-
2
pounds resulting in a limited set of
compounds that potentially represented a
wide range of variation in each removal
mechanism.
Compounds ultimately studied in this
project are:
• Stripping: toluene, 1,4-dichloroben-
zene, methyl ethyl ketone, phenol
• Sorption: phenol, 1,4-dichloroben-
zene, pentachlorophenol
• Bio-oxidation: phenol, toluene, aniline,
2,4-dichlorophenol (very limited test-
ing)
• Laboratory scale activated sludge:
phenol, toluene, aniline, pentachloro-
phenol (biological rates minimized)
A waste stream was selected that
possessed time based uniformity. Pulp
and paper mill foul condensate is a
distillate of the liquor from the pulping
process and is relatively uniform in
composition over time. The focus of this
study was to determine methods to
predict fates of organic compounds added
to this wastewater, not to determine the
treatability of a specific industrial waste
stream.
Biologically inactive (nonviable) biomass
was required for conducting experiments
on the biological sorption of organics.
Five techniques were tested: gamma
irradiation, formaldehyde treatment, ly-
ophilization, lyophilization followed by dry
heating, and lyophilization followed by
exposure to UV light. Biomass from the
acclimation reactors was used in all
experiments. Of the' methods tested, the
most desirable was lyophilization of act-
ivated sludge followed by dry heating at
105°C for 3 hours. This method produced
a stable, dry product that upon rehydration
retained the physical flocculation and
settling properties of the viable biomass
and appeared to have a long shelf life.
Stripping, sorptive, and bio-oxidative
fates of the test chemical of interest were
determined for batch, fill-and-draw, and
continuous laboratory-scale activated
sludge (LAS) reactor conditions. Conven-
tional analytical techniques using chro-
matographic procedures and radiochem-
ical tracers were used to determine
influent and effluent chemical concentra-
tions, fractions of sorbed and stripped
chemicals, and biological degradation and
transformation products including CO2.
Stripping Predictive Fate
Method Results
Stripping tests were conducted with
experimental equipment as shown in
Figure 1. The system's liquid volume was
about 26 L, and air flows from 2 to 8
L/min were used. The stripping PFM
developed offers a simpler approach for
estimating stripping rates in clean water
and wastewater than other approaches
based on the two-film theory of mass
transfer. This method incorporates the
Henry's law constant (Hc in torr L/g-
mole) and the liquid volume-to-air flow
ratio (V/Qair) to directly yield the stripping
rate constant Kasta) for clean water
systems. Equations predicting the strip-
ping rate constant from the compound
Henry's law constant follow the form of
Ka sta • V/Qa,r = 3.71 x 1CT3 (Hc)1 °45 for a
clean water system. Units are hr~1 for Ka
sta and hr for V/Qa,,. When the dimen-
sionless Henry's law constant(Hi) is used,
the dimension less equation, Ka8VV/QaiI
= H,, is developed. This result, along with
other studies in this area, strongly sug-
gest that the process of stripping from
coarse bubble diffuser systems is a
single-stage equilibrium process.
The presence of surfactants, salts, oils,
and nonviable biomass was found to vary
the stripping rate, but in no case was the
effect more than 50% when compared
with that of clean water. The effect
seemed to be the strongest for the higher
volatility compounds.
The values of the stripping rate con-
stant, Ka sta, predicted from the model
developed in this study, seem to agree
reasonably well with previously reported
values. This suggests the possibility of
application beyond the compounds stud-
ied herein.
The stripping PFM was tested in con-
tinuous LAS units. The measured toluene
stripping rate was found to be consistent
with the predicted toluene stripping rate
constant. This further substantiates that
the stripping PFM may be useful for
prediction of compound stripping in con-
tinuous "real world" systems.
Biomass Sorption Predictive
Fate Method Results
Sorption experiments were conducted
to determine sorption kinetic rate con-
stants and equilibrium relationships be-
tween aqueous phase concentration and
loadings onto biological solids for three
test compounds. Test compounds were
chosen to span a wide range in potential
for sorption as indicated by the octanol-
water partition coefficient (Kow). Com-
pounds that were studied include phenol
(Kow = 31), 1,4-dichlorobenzene (Kow =
2455), and pentachlorophenol (associated
form, Kow = 132,000; dissociated form at
pH = 7, Kow = 7,700). All octanol-water
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partition coefficients in this summary are
unitless ratios of equilibrium compound
concentrations in the octanol and water
phases.
Tests with phenol and 1,4-dichloro-
benzene indicate that equilibrium was
reached in less than 15 minutes. Penta-
chlorophenolsorption appears to follow a
two-step process, with a very rapid initial
sorption step and subsequent slower
approach to equilibrium.
For batch testing where sorption is the
sole removal mechanism, the equilibrium
aqueous concentration and substrate
loading on biomass may be expressed:
Cae =
(K0*XfL/1000pL)+1
C, =
where:
Cae - equilibrium aqueous phase sub-
strate concentration (//g/L)
Cs = solids loading on biomass (yug/g)
Cao = initial aqueous phase substrate
concentration (//g/L)
Kow = unitless concentration ratio octa-
nol/water partition coefficient
X = solids (biomass) concentration
(mg/L, dry basis)
fL = lipid weight fraction of biomass
PL = lipid density (g/L)
Table 1 presents a summary of the
measured and predicted endpoint (equil-
ibrium) values of Cae for the sorption
experiments. Table 2 presents measured
and predicted percent removals calcu-
lated from data in Table 1 and the starting
concentrations. Table 3 presents meas-
ured and predicted loadings (Cs).
Generally, good agreement is seen
between measured and predicted values.
Exceptions occur for experiments SP-1
and 2, the start-up experiments, and SP-6
where the mixing intensity was reduced
and the experiment was run at 4°C.
Bio-oxidation Kinetic
Measurements
The contribution of bio-oxidation to
predictive fate assessment of organic
pollutants in industrial waste treatment
was determined for batch, fill-and-draw,
and continuous LAS bioreactors. Bio-
oxidation of specific pollutants was meas-
Wat er In
To Gas
Nitrogen In
Sampling System
(Figures 5, 6, and 7)
Symbols
PR—Pressure Reducer
R—Regulator
FE—Rotameter
TE— Thermometer
D—Drain
SP—Sample Port
PSV—Pressure Relief Valve
DO—Dissolved Oxygen Probe
PI—Pressure Indicator
Air In
Dew Point
Hygrometer
Manometer
Figure 1. Apparatus Used in the Stripping Experiments
ured in activated sludge samples under
batch assay conditions. Mineralization
(oxidation to C02) of 14C-labeled pollutants
was chosen as a primary and unambig-
uous measurement of bio-oxidation.
Qualitative and quantitative measure-
ments of specific degradative bacterial
populations comprising the activated
sludge were performed. These measure-
ments and associated enzymatic activites
were used to evaluate the potential for
describing bio-oxidation kinetics as a
function of the biological community. In
addition, the potential for predicting qual-
itative and quantitative pollutant fate
relative to sludge composition and activity
was investigated.
Laboratory-Scale Activated
Sludge Study
The purpose of this study was to
quantify the removal mechanisms of four
organic substrates in continuous flow,
completely mixed activated sludge units.
Two 11-L LAS units were operated at
mean cell residence times of approxi-
mately 5 and 10 days. These data were to
be used to test the predictive fate methods
that had previously been developed for
stripping, sorption, and bio-oxidation.
Material balances around the activated
sludge units revealed that the fate of
phenol and aniline are almost identical,
with >99.8% of the parent compound bio-
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Table 1. Comparison of Measured and Predicted Sorption Endpoint Concentrations for Batch
Experiments
Measured Predicted
Concentration Concentration' Percent"
Compound Experiment (mg/L) fmg/L) Deviation
Phenol SP-3
SP-4
SP-5
SP-6
1,4-Dichlorobenzene SP-1
SP-2
SP-10
SP-11
Pentachlorophenof SP-7
SP-8
SP-9
SP-11
73.0
73.3
71.8
76.8
26.6
54.2
13.9
2.7
0.8
1.5
0.3
0.7
74.2
74.6
72.8
75.7
17.8
33.8
14.3
3.5
0.91
1.22
0.78
0.99
-1.6
-1.8
-1.4
1.4
33.0
37.6
2.9
-29.6
-13.8
18.7
-160
-41.4
"Where fL - 0.2 and PL = 900 g/L.
"Percent deviation = (measured value - predicted value) -f- measured value x 100.
cPentachlorophenol partially ionized at pH = 7, Kow = 7700.
Table 2. Comparison of Measured and Predicted Sorption Percent Removal
Compound
Phenol
1 ,4 -Dichlorobenze ne
Pentachlorophenof
Experiment
SP-3
SP-4
SP-S
SP-6
SP-1
SP-2
SP-10
SP-11
SP-7
SP-8
SP-9
SP-11
Measured
Removal f%)
4.6
5.8
3.9
1.3
43.0
30.0
72.7
78.7
86.9
76.9
97.2
92.2
Predicted
Removal* (%)
3.0
4.1
2.5
2.7
61.9
56.4
72.0
72.4
85.1
81.2
92.7
89.0
Difference"
(%)
1.6
1.7
1.4
-1.4
-18.9
-26.4
0.7
6.3
1.8
-4.3
4.5
3.2
"(initial concentration - endpoint concentration) 4- initial concentration x 100.
"Difference = measured removal - predicted removal.
cPentachlorophenol partially ionized at pH = 7. /fow = 77OO.
Table 3. Comparison of Measured and Predicted Loading for Sorption Batch Experiments
Compound Experiment
Phenol SP-3
SP-4
SP-5
SP-6
1,4 -Dichlorobenzene SP- 1
SP-2
SP-10
SP-11
PentachlorophenoP SP-7
SP-8
SP-9
SP-11
Measured
Loading
(mg/g)
0.8
0.7
0.8
0.3
6.7
9.8
7.9
2.7
1.6
2.0
1.4
1.7
Predicted
Loading'
(mg/g)
0.5
0.5
0.5
0.5
9.7
18.4
7.8
1.9
1.6
2.1
1.3
1.7
Percent
Deviation
37.5
28.6
37.5
-66.7
-44.8
-87.8
1.3
29.6
1.9
-4.0
5.0
0.6
*C, Values
"Pentachlorophenol partially ionized at pH = 7, /Cow = 7700.
oxidized and stripping losses below de-
tectable limits. Approximately 56% of the
feed 14C phenol was recovered as 14COz
for both compounds. Removal of these
compounds from activated sludge units
by sorption is insignificant on a material
balance basis, with average compound
loadings of <84 /ug/g MLSS and 28 /ug/g
MLSS determined for phenol and aniline,
respectively.
Biological oxidation was also deter-
mined to be the major removal mechan-
ism for the toluene, the most volatile of
the test compounds. Approximately 67%
to 70% of the feed toluene 14C was
recovered as 14CO2 and only 5% to 6% of
the 14C was recovered as soluble metabo-
lites. The ability of the activated sludge
systems to biologically degrade toluene
was found to be very sensitive to devia-
tions from steady-state operating condi-
tions (flow fluctuations, etc.). Grab sam-
ples of mixed liquor indicated variations
in the concentration of toluene in the
aqueous phase to range from <0.05 mg/L
to 4.7 mg/L.
Pentachlorophenol was found to be
extremely resistantto biological oxidation
and stripping. Sorption onto sludge was
determined to be the major removal
mechanism, with both 14C analyses and
Pentachlorophenol analysis indicating
that 6% to 8% of the feed pentachloro-
phenol was removed through sorption to
waste solids. The average pentachloro-
phenol loading on biological solids was
determined to be 1967 pg/g MLSS and
1801 ug/g MLSS for reactors 1 and 2,
respectively.
The predictive fate method, which was
developed for stripping, was determined
to be accurate in predicting the concen-
tration of test compounds in the vent gas
as a function of the measured concen-
tration in the aqueous phase, the Henry's
law constant, and the relative air flow/
liquid volume ratio. Vent gas concentra-
tions of toluene predicted from daily
average data were within ±50% of ob-
served values for approximately 70% of
the observations. The remaining observa-
tions had either or both vent gas and/or
mixed liquor concentrations below the
detection limit.
Average loading of aniline, phenol, and
Pentachlorophenol onto biological solids
were found to be related to the octanol-
water partition coefficient. However, the
proposed predictive equation for relating
equilibrium loading to the equilibrium
aqueous phase concentration was found
to predict loadings that were lower than
those observed for aniline, an ionizable
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compound. Conversely, predicted penta-
chlorophenol loadings were seven-fold
higher than those observed.
Overall Mathematical Predictive
Fate Method
An overall mathematical PFM was
developed to predict the equilibrium
aqueous phase concentration in the
secondary effluent from a completely
mixed activated sludge system. The strip-
ping PFM and the equilibrium sorption
PFM for substrates at low concentrations
are incorporated into traditional "uniform
biomass" design models taken from
environmental engineering. This equa-
tion, and its derivation, is given in the
project report.
Conclusions
This work represents a broad overview
assessing the feasibility of using both
experimental and mathematical predic-
tors to quantitatively determine fates.
Methodology using chemical engineering
kinetic approaches and reactor-design
equations appears to be a viable way to
analyze multi-mechanism processes for
various reactor configurations.
The data base existing at the beginning
of this effort was limited because of the
specific emphasis given to different ques-
tions in each study and to the past focus
on removal as opposed to specific chem-
ical fates. Some indications on relative
fate processes may still be drawn, partic-
ularly from more recent studies that look
at numerous compounds with the same
experimental protocol.
Stripping in completely mixed, diffused
air systems has been found to be essen-
tially an equilibrium process, and predic-
tive equations are proposed. Verification
on other compounds and system config-
urations is suggested. The effects of
contaminants(surfactants, salts, oils, and
nonviable biomass) are significant on
oxygen transfer rate constants and less
significant on stripping transfer process-
es. Stripping rate estimates based on
oxygen transfer rates for contaminated
waters such as treatment plant mixed
liquors must be questioned.
Sorption was quantified in a variable-
volume batch reactor using nonviable
biomass and later in continuous labor-
atory activated sludge studies. An equil-
ibrium deterministic predictive equation
is proposed for low aqueous concentra-
tions. Kinetic sorption rates for the com-
pounds studied could not be quantified
because of their rapidity compared "with
the time required for sampling and anal-
ysis.
Numerous kinetic rate constants for
biological processes exist and can be
formulated. Each of these rates applies to
specific cases in substrate and biomass
concentration and reactor configuration.
Little reliable data exist in this area, and
accepted overall methodologies are lack-
ing. First- and second-order (first order in
both substrate and biomass concentra-
tion) rate constants are developed in this
study for batch, fill-and-draw, and contin-
uous reactor configurations for the com-
pounds studied. Disappearance rates
were calculated, but mineralization rates
were emphasized. Mineralization pro-
vides an unambiguous predictor of bio-
degradation, but disappearance kinetics
are required for fate predictive equations.
Mineralization rates for the compounds
studied were generally comparable over
the batch, fill-and-draw, and continuous
reactor configurations. However, disap-
pearance rate kinetics were comparable
only for batch and fill-and-draw systems
and ranged from 2 to 3 orders of magni-
tude slower than those demonstrated in
the steady-state continuous systems. The
batch and fill-and-draw kinetic disap-
pearance values are of the same order as
data reported in the literature for specific
compounds and BOD.
Laboratory-scale activated sludge sys-
tems were designed and operated to
elucidate compound fates in a conclusive
fashion. This included the use of radio-
labeled substrate in conjunction with
nonlabeled substrate and sampling of all
streams of fate importance. Many of these
procedures are substantially more diffi-
cult to implement in full-scale processes.
Full-scale fate data cannot, therefore, be
as precise or conclusive as the more
controlled experiments.
A coupled, algebraic, predictive fate
equation is presented subject to assump-
tions and derivations given in the project
report. An example of organic compound
fates is provided by assuming most
probable, maximum, and minimum values
for the equation variables and using
biological rate constants calculated from
other studies. Generally, the most prob-
able values agree with the findings in this
study, and the ranges agree with full-
scale plant studies implemented by EPA.
The full report was submitted in fulfill-
ment of Contracts No. 68-03-3027 and
68-03-3074 by IT Corporation and the
University of Tennessee (subcontract)
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
U. S. GOVERNMENT PRINTING OfFICE: 1985/646-116/20718
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J. W. Blackburn, W. L. Troxler, K. N. Truong, R. P. Zink. S. C. Meckstroth, J. R.
Florence, and A. Groen are with IT Corporation, Knoxville, TN 37923; G. S.
Sayler, R. W. Beck, R. A. Mi near, and A. Breen are with University of Tennessee,
Knoxville, TN 37916; and O. Yagi is with National Institute for Environmental
Studies, Yatabe, Japan.
R. J. Turner is the EPA Project Officer (see below).
The complete report, entitled "Organic Chemical Fate Prediction in Activated
Sludge Treatment Processes," (Order No. PB 85-247 674; Cost: $28.95, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S2-85/102
0000329 PS
U S FNVIR PROTECTION AGENCY
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230 S DEAR30RN STREET
CHICAGO U- 60604
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